The present invention relates to the general technical field of appliances for steam cooking, such as pressure cookers for example, in which a lid is locked to a pot in a sealed manner by the intermediary of a peripheral sealing joint.
The present invention concerns more particularly an automatic pressure limiting safety device for a container, such as a pressure cooker, the safety device comprising a sealing joint interposed between the pot and lid of the container, the joint having at least one length portion which presents an external clearance forming a weakened transverse cross section to permit a deformation of the joint in that portion under the action of the internal operating pressure, starting from a predetermined value of the pressure, to assure a gap in the seal and thus depressurization of the container.
The present invention equally concerns a pressurized container, and in particularly a pressure cooker, equipped with a safety device according to the invention.
In containers for steam cooking in a closed atmosphere, such as pressure cookers, it is necessary to provide a safety device capable of assuring, in case of a malfunction of the main pressure control system, an escape of steam upon attainment of a pre-established pressure corresponding to an assigned pressure.
It is already known in devices according to the prior art to install a sealing joint, or seal, under compression between the pot and the lid of a container. Such a joint assures, when the lid is locked, for example by a closing device of the bayonet-type, a complete seal for the container. In case of an excessively high pressure and simultaneously a failure of the main pressure regulating system, a break in the integrity of the sealing joint is assured by a radial and localized deformation of the joint in a space formed by a groove or recess formed in the edge or the peripheral skirt of the lid. Deformation of the joint into this space permits an interruption of the sealing effect between the upper edge of the pot and the joint itself, which permits vapor to escape. Such systems are described, for example, in U.S. Pat. No. 2,600,703 and Swiss Pat. No. 407,459.
Other known safety systems for assuring automatic depressurization of a container under pressure are described in U.S. Pat. No. 4,276,990 and British Pat. No. 2,208,131. These systems provide for the interposition of a sealing joint between the pot of a container and its lid. They include, in addition, an extrusion opening arranged in the lid, in particular in its peripheral skirt.
In case of an excessive pressure, or over pressure, the joint can be extruded through the opening of the lid in a manner to permit steam to leak toward the bottom along the side of the pot. Extrusion of the joint through the opening of the lid can be aided by providing an internal clearance in the joint, such as described, for example, in Swiss Pat. No. 571,335.
Such a system can be improved by providing, substantially in front of the extrusion opening, a creep hole that extends through the lid. In such a case, during extrusion of the joint through the lateral opening of the lid, steam can escape via the lid, because the joint then uncovers the creep hole. This improvement prevents escape of the vapor toward the bottom, which could have as its effect to extinguish the heating source when the latter is constituted by gas.
Other known arrangements include, as disclosed for example in U.S. Pat. No. 2,600,714, depressurization safety devices comprising an annular joint presenting a clearance in its external face. Such a joint is mounted on a pressure cooker between the lid and the pot. It presents a weakened transverse section and is deformed at the level of the external clearance in the case of an excessive pressure in order to create a break in the seal.
The totality of automatic depressurization safety devices described above fulfill, in a generally satisfactory manner, their assigned safety function. They have been found, however, to present a certain number of drawbacks including, among the most significant, the necessity for a specific design for the lid. The lid must, in effect, have an outline adapted in a localized manner to permit the joint itself to deform locally either in grooves, or through extrusion openings. Such arrangements of the outline of the lid introduce extra steps in the industrial fabrication process and render that process more complex to the extent that additional constraints and tolerances are introduced. The overall cost of these arrangements is moreover not negligible, which finally results in a general increase in the final cost of the product. Moreover, the known joints are often extruded between sides and the liberation of steam is effectuated abruptly, rather than progressively, entailing risks of spraying and of extinction of the cooking fire.